(1) Field of the Invention
The invention relates to a guiding and pressing device for a sand belt, and more particularly to a device used in a belt sander to prevent a sand belt from skewing and to ensure the sand belt to be always in a tightened state.
(2) Description of the Prior Art
A belt sander having a sand belt, which is rotated at a high speed to sand or polish a wood surface, has been described in U.S. Pat. No. 7,025,666 to this applicant, in which some drawbacks in this kind of conventional sander have been improved. Thus, the sand belt in the belt sander may be replaced quickly, and the improvements on the absorption of the powder and chips or on the sanding effect of the workpiece, and on the lengthening of the lifetime of the sand belt can be obtained. However, this kind of sander still has some defects, which bring the inconvenience to the user in practical usage for many years.
First, when the sand belt is rotated at the high speed continuously, it is possible to cause the inconsistency in the reaction force due to the unsmooth wood surface contacting the sand belt or the uneven hardness of the wood surface contacting the sand belt. In addition, the sanding mechanism itself swings in a reciprocating manner, so the sand belt is laterally biased after a period of sanding time. If the sand belt is biased to a predetermined degree, the effect of sanding the wood may be influenced. In this case, the operator has to stop the machine and loosen and reset the sand belt, and then to tighten the sand belt to continue the sanding operation. Thus, the complicated operations have to be repeated after a predetermined period of time. In addition to the increase of the trouble of the operation, the sand belt may be broken to cause the extra loss.
Second, when the sand belt is rotated at the high speed, it must be in the tightened state so that the wood can be effectively sanded and polished. However, when the sand belt continuously sands the wood for a period of time, the sand belt naturally becomes loose so that the operator has to stop the machine every predetermined period of time, and then to adjust the distance between two transmission shafts to tighten the sand belt again. Thus, the sanding operation can be continued, but the operations are complicated.